The present invention relates to catheters designed for delivery of therapeutic substances in vivo. More specifically, the present invention relates to catheters designed for intravascular delivery of therapeutic radiation in vivo.
Isotopic radiation therapy has been proposed for the treatment of various vascular disorders, such as restenosis following angioplasty. Prior to the present invention, it was believed that gamma emitting isotopes would be useful for peripheral brachy therapy. However, the use of gamma emitting isotopes poses a great deal of logistical difficulty in safely delivering the isotope.
The use of beta emitting isotopes would be easier and safer for vascular brachy therapy because beta emitting isotopes have relatively low penetrance and are easier to shield. However, the use of beta emitting isotopes is limited by the penetrating depth, which is about 3-4 mm at the appropriate doses required for intervention. Many arteries are larger than 3-4 mm, for example measuring 5 to 7 mm in diameter in the superficial femoral artery and even larger in the aortoiliac system.
What is needed is a device for intravascular delivery which allows for the use of radiation emitting isotopes in larger diameter vessels, and which minimizes the safety precautions required by gamma emitting isotopes.
The present invention provides a device, and methods of use thereof, for the targeted delivery of radiation in vivo. The therapeutic radiation delivered by the device of the present invention can be used, for example, to prevent restenosis after angioplasty. The catheter of the present invention is especially suited for such treatment because it substantially aids in the delivery of radiation to an intravascular treatment site.
Further, the device of the present invention makes it possible for beta emitting isotopes to be used as sources of therapeutic radiation. The use of beta emitting isotopes is advantageous because they have low penetrance, e.g., in the range of 3-4 mm, and they are relatively easy to shield. Prior to the present invention, the low penetrance of the beta emitting isotopes has limited their usefulness in treating vascular sites because many vascular sites exceed in size the penetrance of beta emitting isotopes. By using the beta emitting isotopes in conjunction with the catheter of the present invention, this problem can be overcome by placing the beta emitting isotope at the vascular site. The present invention further overcomes this problem by placing the beta emitting isotopes in channels located on the periphery of an inflatable balloon connected to the end of the catheter. This balloon also increases the accuracy of the treatment delivery by immobilizing the catheter tip at the treatment site.
The present invention can also provide greater control over radiation delivery by providing a return channel for the radiation emitting isotopes rather than merely a blind port. Such a return channel allows for greater control of the treatment duration, as well as greater flexibility in dosing regimens. Further, the path of such return channels can also contribute to the radiation delivery.
The present invention allows delivery of isotopes via several methods. These include, but are not limited to, radioactive wires, radioactive seed trains, radioactive gases and liquids, as well as other radiation emitting materials known to one skilled in the art. Preferably, the present invention utilizes beta emitting isotopes, but other types of radiation emitting materials may be used and is contemplated as within the scope of the present invention. Examples of beta emitting isotopes used with the present invention are 90strontium, 125iodine, 192iridium, itrium, 188rhenium, 186rhenium and 133xenom.
In another embodiment of the present invention, the catheter can also include a radiation shielding. Such shielding is used to increase the accuracy and safety of the radiation delivery by preventing undesired radiation emission from the delivery channels. Further, radiation shielding can be used in the present invention to avoid the necessity of complex afterflow devices. For example, radiation emitting isotopes can be situated within radiation shielding inside the catheter. Once the catheter is in place, the radiation emitting isotopes can be exposed. This can be accomplished, alternatively, by moving the shielding or by moving the radiation emitting isotopes, such that the radiation emitting isotopes are no longer shielded.
The present invention can also take the form of a double catheter system. In this embodiment of the present invention, the inner, shielded catheter contains a movable radiation emitting source. The radiation emitting source can be, for example, an irradiated wire or a series of radiation emitting pellets embedded in a plastic wire matrix. The wire can be movable such that it can be extended beyond the distal end of the radiation shielding. The present invention also provides that this shielded catheter can have a radiation proof valve located on its distal tip. An outer catheter can contain two lumens: an eccentrically located guide wire lumen and a large lumen sized to receive the inner, shielded catheter. The shielded catheter can be inserted into the outer catheter prior to insertion of the catheter system in vivo. Once the catheter has been properly placed in vivo, the radiation emitting wire can be extended beyond the shielding to complete the delivery of the radiation to the treatment site.
Such a system can provide a number of advantages. For example, the outer catheter can be disposable. Additionally, the shielded catheter can be used to store the radiation emitting source between uses. Such a system also avoids the necessity of complex afterflow devices.
The present invention can also comprise a method of delivering radiation to an in vivo treatment site using a catheter. This method can comprise the steps of inserting the catheter until it is properly positioned in vivo; delivering the radiation emitting isotopes through the catheter or unshielding the radiation emitting source within the catheter; allowing the radiation treatment to continue for the appropriate amount of time; and then removing and/or reshielding the radiation emitting source.
Accordingly, it is an object of the present invention to provide catheters and methods that can safely and accurately deliver radiation emitting substances to a desired site.
It is another object of the present invention to provide catheters and methods that can safely and accurately deliver beta radiation emitting isotopes to a desired site.
It is another object of the present invention to provide a catheter and method that can be used to locally treat a diseased area using radiation.
It is another object of the present invention to provide a catheter and method that can be used to treat an intravascular site using radiation.
It is another object of the present invention to provide a catheter and method that can be used to treat restenosis.
It is another object of the present invention to provide a catheter and method that can be used to increase the therapeutic effectiveness of beta emitting isotopes by delivering them such that the distance between the beta emitting isotopes and the treatment site is less than the penetrance of the beta emitting isotopes.
It is another object of the present invention to provide a catheter and method that can be used to increase the effectiveness and safety of radiation therapy by utilizing radiation shielding.
These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.